This invention relates to an apparatus for handling mail articles such as post cards and envelopes, and more particularly to an overlapped-transfer detecting apparatus which detects that a plurality of mail articles are overlapped while they are being transferred.
In a mail handling apparatus, mail articles should be transferred individually, i.e., piece-by-piece. When a plurality of mail articles are fed together to the handling apparatus, in an overlapped manner, the handling apparatus can not perform its normal operation and encounters trouble, such as a jam.
According to a prior art overlapped-transfer detecting apparatus, a shifting device is provided in a transport path of a mail article. Such a shifting device is composed of two rollers, one of which is rotated at a speed which is different from the transfer speed, the other roller being idly rotated. Overlapped mail articles are shifted relative to each other when they are passed between the two rollers, because one mail article engaging the rotated roller has a speed which is different from the transfer speed. The one article is accelerated or decelerated as compared with the other mail article engaging the idle roller, which maintains its transfer speed. In addition to the shifting device, two length-measuring devices are provided before and after the shifting device, along the transport path. If the length of the mail article measured by the upstream measuring device is not equal to the length measured by the downstream measuring device, the overlapped-transfer is detected. As a result, in a mail handling apparatus, the overlapped mail articles are rejected or fed to a separating apparatus.
However, if the apparent length of the overlapped mail articles is not changed after the shifting operation, the prior art detecting apparatus can not detect the overlapped-transfer. In practice, when rectangular envelopes are transferred in the longitudial direction in a mail handling apparatus, some envelopes are frequently turned up and become in an up-standing state. The up-standing envelope is easily overlapped on another longitudially-transferred one. In this case, the width of the up-standing envelope is entirely behind the length of the non-up-standing envelope. This relationship is sometimes not changed even after the two envelopes are shifted, so that the shifting operation can not change the length of overlapped mail articles in the transfer direction. When two envelopes strongly adhere to each other, the length of the overlapped envelopes is not changed even by the shifting operation.